Field of the Invention
The invention relates to an apparatus for conversion of a three-phase voltage system into an electrically isolated DC voltage to be predetermined freely, including a primary circuit and a secondary circuit, each phase of the primary circuit having a series inductance connected to one input of an associated bidirectional, bipolar electronic switching apparatus having directly connected respective second inputs, a positive primary voltage rail fed through diodes, and a negative primary voltage rail fed through other diodes. The invention also relates to a method for controlling the apparatus.
According to the present prior art, a converter circuit and a control device known from European Patent Application EP 0 660 498 and having a downstream DC-voltage converter stage, is preferably used to provide a three-phase pulsed rectifier system to meet a requirement for current taken from a three-phase mains system to have an approximately sinusoidal profile, for the mains system response at the fundamental frequency to be resistive, and to provide potential isolation and the capability of controlling the output DC voltage.
However, voltage intermediate-circuit converter systems which are formed in that way have a power section with a relatively complex structure and relatively low efficiency, since the energy conversion takes place in two stages, and the overall efficiency is thus governed by the product of the efficiency elements.
Furthermore, the capacitors which have to be provided to buffer the intermediate-circuit voltage increase the physical size of the system, and reduce its power density.